Respiratory health effects of exposure to low-NOx unflued gas heaters in the classroom: a double-blind, cluster-randomized, crossover study

Environ Health Perspect. 2010 Oct;118(10):1476-82. doi: 10.1289/ehp.1002186. Epub 2010 Jul 20.


Background: There are long-standing concerns about adverse effects of gas appliances on respiratory health. However, the potential adverse effect of low-NOx (nitrogen oxide) unflued gas heaters on children's health has not been assessed.

Objectives: Our goal was to compare the respiratory health effects and air quality consequences of exposure to low-NOx unflued gas heaters with exposure to non-indoor-air-emitting flued gas heaters in school classrooms.

Methods: We conducted a double-blind, cluster-randomized, crossover study in 400 primary school students attending 22 schools in New South Wales, Australia. Children measured their lung function and recorded symptoms and medication use twice daily. Nitrogen dioxide (NO2) and formaldehyde concentrations were measured in classrooms using passive diffusion badges.

Results: NO2 concentrations were, on average, 1.8 times higher [95% confidence interval (CI), 1.6-2.1] and formaldehyde concentrations were, on average, 9.4 ppb higher (95% CI, 5.7-13.1) during exposure to unflued gas versus flued gas heaters. Exposure to the unflued gas heaters was associated with increased cough reported in the evening [odds ratio (OR) = 1.16; 95% CI, 1.01-1.34] and wheeze reported in the morning (OR = 1.38; 95% CI, 1.04-1.83). The association with wheeze was greater in atopic subjects. There was no evidence of an adverse effect on lung function.

Conclusions: We conclude that classroom exposure to low-NOx unflued gas heaters causes increased respiratory symptoms, particularly in atopic children, but is not associated with significant decrements in lung function. It is important to seek alternative sources of heating that do not have adverse effects on health.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Child
  • Cross-Over Studies
  • Double-Blind Method
  • Heating*
  • Humans
  • New South Wales
  • Nitrogen Oxides / adverse effects*
  • Respiratory Function Tests
  • Respiratory System / drug effects*
  • Respiratory System / physiopathology
  • Schools*


  • Nitrogen Oxides